Add default_visibility for soong modules

So that we don't get surprise usages.

Bug: 348717861
Test: m nothing
Change-Id: I47319a727092c1bd936cca88f5713ee977a48b48
diff --git a/testing/code_metadata_internal_proto/Android.bp b/testing/code_metadata_internal_proto/Android.bp
index a534cc2..396e44f 100644
--- a/testing/code_metadata_internal_proto/Android.bp
+++ b/testing/code_metadata_internal_proto/Android.bp
@@ -20,10 +20,14 @@
     name: "soong-testing-code_metadata_internal_proto",
     pkgPath: "android/soong/testing/code_metadata_internal_proto",
     deps: [
-            "golang-protobuf-reflect-protoreflect",
-            "golang-protobuf-runtime-protoimpl",
-        ],
+        "golang-protobuf-reflect-protoreflect",
+        "golang-protobuf-runtime-protoimpl",
+    ],
     srcs: [
         "code_metadata_internal.pb.go",
     ],
+    visibility: [
+        "//build/make/tools/metadata",
+        "//build/soong:__subpackages__",
+    ],
 }